Spatial distribution of ground motion data of recent earthquakes unveiled some features of peak ground acceleration (PGA) attenuation with respect to closest distance to the fault ͑R͒ that current predictive models may not effectively capture. As such, PGA: (1) remains constant in the near-fault area, (2) may show an increase in amplitudes at a certain distance of about 3-10 km from the fault rupture, (3) attenuates with slope of R −1 and faster at farther distances, and (4) intensifies at certain distances due to basin effect (if basin is present). A new ground motion attenuation model is developed using a comprehensive set of ground motion data compiled from shallow crustal earthquakes. A novel feature of the predictive model is its new functional form structured on the transfer function of a single-degree-of-freedom oscillator whereby frequency square term is replaced with closest distance to the fault. We are proposing to fit ground motion amplitudes to a shape of a response function of a series (cascade) of filters, stacked separately one after another, instead of fitting an attenuation curve to a prescribed empirical expression. In this mathematical model each filter represents a separate physical effect.
S U M M A R YNear-surface properties play an important role in advancing earthquake hazard assessment. Other areas where near-surface properties are crucial include civil engineering and detection and delineation of potable groundwater. From an exploration point of view, near-surface properties are needed for wavefield separation and correcting for the local near-receiver structure. It has been shown that these properties can be estimated for a lossless homogeneous medium using the propagator matrix. To estimate the near-surface properties, we apply deconvolution to passive borehole recordings of waves excited by an earthquake. Deconvolution of these incoherent waveforms recorded by the sensors at different depths in the borehole with the recording at the surface results in waves that propagate upwards and downwards along the array. These waves, obtained by deconvolution, can be used to estimate the P-and S-wave velocities near the surface. As opposed to waves obtained by cross-correlation that represent filtered version of the sum of causal and acausal Green's function between the two receivers, the waves obtained by deconvolution represent the elements of the propagator matrix. Finally, we show analytically the extension of the propagator matrix analysis to a lossy layered medium for a special case of normal incidence.Near-surface properties are useful in quantifying seismic hazards. These properties are important for applications, such as civil engineering and groundwater detection. The variability of the near-surface properties is caused by changes in porosity, permeability, fractures, fluids, compaction, diagenesis and metamorphism (Toksöz et al. 1976). The lateral and temporal variations in the near-surface properties are a major cause of poor repeatability of the source radiation pattern (Aritman 2001), and hence reduce the repeatability of time-lapse surveys. Knowledge of these near-surface properties is, hence, crucial for time-lapse monitoring. The local near-surface properties are also required to determine the free-surface reflectivity which is useful to perform wavefield decomposition (Dankbaar 1985;Wapenaar et al. 1990). Estimation of the near-surface properties for a lossless homogeneous medium using the propagator matrix and wave-equation inversion is shown for SH waves by Trampert et al. (1993) and for P-SV waves by van Vossen et al. (2004). Wapenaar et al. 2005;Snieder et al. 2006a) is a technique based on combining signals recorded at different sensors, to estimate the response between them. Until recently cross-correlation is a widely used tool for applying seismic interferometry. Instead of cross-correlation, deconvolution can also be used as a seismic interferometric tool (Snieder & Ş afak 2006;Vasconcelos & Snieder 2006). To estimate the nearsurface properties, we apply deconvolution to borehole recording of earthquake data. Deconvolution of the incoherent waveforms recorded by the sensors at different depths in the borehole with the recording at the surface results in waves that propagate ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.